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Learn you a Haskell for Great Good!

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What is Haskell?

When you are starting out in Haskell, you need keep these items in your mind:

  1. Purely function programming language: f(x) => g, if it is called twice with the same parameters x, it is guaranteed to return the same result g
  2. Lazy
  3. Statically Typed: It means type inference, you don’t explicitly state their type.

Run ghc’s interactive mode to Get a very basic feel for Haskell

Operators

  1. simple arithmetic

    +, -, *, /; if we want to have a negative number, it’s always best to surround it with parentheses. like 5 * (- 3)

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    $ ghci
    GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help  
    Loading package base ... linking ... done. 
    prelude>
    # +-*/
    $ ghci> 2 + 15
    17
    $ ghci> 49 * 100
    4900
    $ ghci> 5 / 2
    2.5
    $ ghci> 50 * 100 - 4999
    1
    # use parentheses to change it
    $ ghci> 50 * (100 - 4999)
    -244950
    $ ghci> 5 * - 3 # ❌
    $ ghci> 5 * (- 3) # ✅
    -15

  2. Boolean algebra: True, False, &&, ||, not

    equality: ==, /=. what about doing 5 + "llama" or 5 == True ? we will get a big error message! Don’t do that!

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    $ ghci> True && False
    False
    $ ghci> True && True
    True
    $ ghci> False || True
    True
    $ ghci> not False
    True
    $ ghci> not (True && True)
    False
    $ ghci> 5 == 5
    True
    $ ghci> 1 == 0
    False
    $ ghci> 5 /= 5
    False
    $ ghci> 5 /= 4
    True
    # but we can do 5 + 4.0
    $ ghci> 5 + 4.0 # 5 can act like an integer or a floating-point number. 
    9.0

function: prefix, infix

prefix function

prefix function like succ function takes anything that has a defined successor and return that successor. it means it can increase the parameter(like numbers).
also, The functions min and max take two things that can be put in an order(like numbers).

succ, min, max
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ghci> succ 8
9
# min returns the one that's lesser
ghci> min 9 10
9
ghci> min 3.4 3.2
3.2
# max return the one that's greater
ghci> max 100 101
101
# Function applications have the highest precedence, as reflected by the fact that when mixed with other operators
# What that means for us is that these two statements are equivalent.
ghci> succ 9 + max 5 4 + 1
16
ghci> (succ 9) + (max 5 4) + 1
16
#  if we wanted to get the successor of the product of numbers 9 and 10, we couldn't write succ 9 * 10
ghci> succ 9 * 10
100
# It is equivalent to
ghci> (succ 9) * 10
100
# we have to write this statement to get 91
ghci> succ (9 * 10)
91

infix function

backticks: `

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# division
# there maybe some confusion as to which number is doing the division and which one is being divided.
ghci> div 92 10
9
# we can call it as an infix function by surrounding it with backticks.
# it's much clearer
ghci> 92 `div` 10
9